In drug delivery there is a need for improved formulation techniques that enables a targeted and/or localised delivery of active drug substances to the body. For instance in the drug treatment of tumours or other diseases in local tissues, procedures and formulations to optimise the local effects of the drugs and reduce the spectrum of side effects are still needed. Drug release implants that are implanted with minimally invasive surgery are also they attractive since they reduce the need for open surgery.
Ceramic substances like e.g. calcium sulphate have been suggested as implant materials for controlled release of active substances (see e.g. Royer U.S. Pat. No. 6,391,336, U.S. Pat. No. 6,630,486, US 2003/0170307). In order to obtain a slower release of the active substance from the ceramics, Royer uses a complexing agent that is a polymeric substance that forms a complex with the active substance, whereby a slower release may be obtained.
However, the present inventors have found another method to adjust the release rate of the active substance, which method involves sealing of the inherent micro-porous structure within the composition in order to ensure that the release primarily takes place via erosion or biodegradation of the implanted composition.
Moreover, a suitable way of controlling the erosion or biodegradation rate is described, based on ensuring a structure of the ceramic characterised by an increased surface area towards to surrounding environment, whereby the erosion or biodegradation of the composition is increased (due to the increased apparent surface area). Accordingly, a better adjustment method is achieved, whereby the primary adjustment factor lies in the more open structure, e.g. a ruptured structure like a foam-like structure or a disintegrated structure, obtained in a composition according to the invention. The increased surface area towards the body fluids and tissues is achieved using additives here referred to as expandable agents.